Cutting tools in the past were run with spears so that the cut tubular string could be retained by the spear and then pulled out of the hole. The cutter designs were variable and many included blades that extend by sliding down a ramp and turning about a pivot that was driven by a piston that was fluid driven and a spring to retract the blades. Some examples of such designs are U.S. Pat. Nos. 5,791,409; 2,136,518; 2,167,739 and US2013/0168076. As to the latter reference, there is no pivoting action as the blades translate radially. With this orientation, the blades have to either extend out below a tubular to be milled or into a recess where another tool has already removed a tubular wall. The illustrated tool is not designed to cut through a wall of a tubular due to its blade orientation. Other styles for cutting tubular strings are illustrated in U.S. Pat. Nos. 7,823,632; 5,018,580; 4,856,642 and 5,014,780.
In the original version of the present invention several issues in the prior design are addressed and a design is presented that is a more reliable and economical. The actuating piston is flow actuated to shift and extend the cutting blades and to retain the extended blade position even after the flow is cut off. The blades are retracted with pressure on a landed plug on the piston so that a return spring is not required. The reverse movement of the piston shears out the body lock ring that had previously held the piston on the blade extended position. When the blades get through the wall of the tubular string being cut the adjacent housing squarely supports the blades that are extended radially so as to better support the cut string with reduced stress on the blades as the cut string is raised up to the point where it can be supported from slips on the rig floor so that the blades can be retracted after slacking off weight and pressuring up against a bumped plug on top of the piston.
As currently envisioned, the cutter blades extend and stay extended as long as pressure on a piston is continued. Instead of cutting off a transition in a tubular that had been expanded and removing the transition to the surface, the blades cut through the wall of a tubular and then mill in an uphole direction to take out a piece of the tubular. The piston that held out the blades when pressure was applied is acted on by a return bias when the pressure is removed so that the blades can retract and the tool removed through the cut tubular. As a backup a plug can be dropped to obstruct a through passage in the piston so that pressure from the surface can be used to force the piston back to retract the blades. In one possible use of the tool, the cut and milled portion can be then blocked off such as with cement for a plug and abandonment of the well.
These and other features will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.